JP2009227754A - Method for producing fluorine-containing copolymer - Google Patents

Abstract

The present invention provides a method for producing a fluorinated copolymer capable of forming an aqueous dispersion having excellent mechanical stability.
SOLUTION: Vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene are substituted with a general formula CF ₃ CF ₂ CF ₂ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COOM (where M is a hydrogen atom, a lithium atom, 2,3,3,3-tetrafluoro-2- [1,1,2,3,3,3-hexafluoro-2- (1,1, 2,2,3,3,3-Heptafluoropropoxy) propoxy] -1-propanoic acid or a salt thereof is used as a surfactant to carry out a copolymerization reaction in an aqueous medium to produce a fluorinated copolymer. According to the method of the present invention, compared to the case of using a conventionally used ammonium perfluorooctanoate emulsifier, an aqueous solution exhibiting excellent mechanical stability even when its use ratio is less than half. A dispersion is formed.
[Selection figure] None

Description

  The present invention relates to a method for producing a fluorinated copolymer. More specifically, the present invention relates to a method for producing a fluorinated copolymer capable of forming an aqueous dispersion having excellent mechanical stability.

It has a copolymer composition of about 70 to 90 mol% vinylidene fluoride, about 2 to 30 mol% hexafluoropropylene and about 1 to 10 mol% chlorotrifluoroethylene, and further contains about 20 mol% or less of tetrafluoroethylene. A fluorine-containing copolymer aqueous dispersion in which a copolymer that can be polymerized is dispersed in an aqueous medium has been proposed by the present applicant, and this aqueous dispersion provides the mechanical stability required for use as a coating material. Satisfied.
Japanese Patent Laid-Open No. 10-120858

Further, it has a copolymer composition comprising 50 to 80% by weight of vinylidene fluoride, 20 to 50% by weight of hexafluoropropylene and 0 to 30% by weight of other copolymerizable monomers such as tetrafluoroethylene, and has an average particle size An aqueous dispersion of fluorine-containing copolymer in which fluorine-containing copolymer particles having a particle diameter of 30 to 200 nm are dispersed in an aqueous medium has also been proposed. This aqueous dispersion has a coating film excellent in weather resistance and stain resistance. Is said to be easily formed and has excellent sedimentation stability.
JP 7-258499 A

  However, the mechanical stability of the obtained fluorine-containing copolymer aqueous dispersion is never satisfactory, and since the solid content concentration is as low as about 30% by weight (each example), it is somewhat coatable. There is also a problem that it is inferior.

Furthermore, the general formula
Rf ¹ O (CFXCF ₂ O) _p CFXCOOM
Rf ¹ : C _{1 to} C ₅ perfluoroalkyl group
X: F, Cl, perfluoroalkyl group C ₁ -C ₄
p: 0-5
M: Fluorine-containing olefin alone or emulsification of fluorine-containing olefin and other monomers in an aqueous medium in the presence of a fluorine-containing surfactant represented by H, alkali metal, alkaline earth metal, or ammonium group A method for producing a fluoropolymer latex by polymerization is proposed.
JP 2003-119204 A

As the fluorine-containing surfactant represented by the above general formula,
CF ₃ CF ₂ CF ₂ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COONH ₄
As specific examples of preferable resinous VdF polymers, VdF / TFE / HFP (45 to 99/0 to 45/1 to 10 mol% ratio) copolymers and the like are mentioned. The obtained fluoropolymer latex contains fluoropolymer particles having a number average particle size of 0.01 to 1 μm, preferably 0.05 to 0.7 μm, at a concentration of about 10 to 40% by weight, preferably 20 to 40% by weight. Patent Document 3 discloses that the dispersion and emulsification state of particles is a latex (aqueous emulsion) and is stable.

  However, the monomer composition for obtaining a thermoplastic elastomer which is a fluoropolymer may be mainly composed of VdF and HFP, and examples of preferred copolymers in this case include VdF / TFE / HFP. Although it has been described, examples of it are not described. In addition, although it is stated that the dispersed and emulsified state of the latex particles is stable as described above, no mention is made of its mechanical stability.

  Fluoropolymers are widely used for coating materials because of their excellent antifouling properties and weather resistance. Fluorine-containing copolymer aqueous dispersions used for this type of application not only have excellent sedimentation stability in practical use, but are also suitable for mechanical processing such as stirring, transfer, metering, pigment mixing, and spraying. Is required to have sufficient stability.

  An object of the present invention is to provide a method for producing a fluorinated copolymer capable of forming an aqueous dispersion having excellent mechanical stability.

The object of the present invention is to combine vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene with the general formula
CF ₃ CF ₂ CF ₂ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COOM
(Wherein M is a hydrogen atom, a lithium atom, a sodium atom, a potassium atom or an ammonium group) 2,3,3,3-tetrafluoro-2- [1,1,2,3,3, 3-hexafluoro-2- (1,1,2,2,3,3,3-heptafluoropropoxy) propoxy] -1-propanoic acid or its salt as a surfactant in a copolymerization reaction in an aqueous medium And achieved by a method for producing a fluorine-containing copolymer. The produced fluorine-containing copolymer is obtained as an aqueous dispersion.

  The obtained fluorine-containing copolymer has a vinylidene fluoride content of 70 to 96 mol%, particularly preferably 87 to 89 mol%, tetrafluoroethylene content of 2 to 20 mol%, particularly preferably 5 to 7 mol%, Hexafluoropropylene has a copolymer composition of 2 to 10 mol%, particularly preferably 5 to 7 mol%.

  The aqueous dispersion of the fluorine-containing copolymer produced by the method of the present invention has an average emulsion particle size in the aqueous dispersion of 30 to 200 nm, preferably 50 to 120 nm, and a solid content concentration of 40 to 50% by weight. High concentration, the average emulsion particle size increase rate after passing this aqueous dispersion 10 times through 325 mesh screen 10 times is less than 10%, and the solid content concentration decrease rate is less than 5% Show mechanical stability.

  The mechanical stability of the fluorine-containing copolymer aqueous dispersion described in Patent Document 1 is also excellent. According to the examples, the reduction rate of the solid content concentration is 1.7% or 1.1%. The increase rate of the particle diameter is 4.0% and 18.3%, and the aqueous dispersion of the fluorine-containing copolymer according to the present invention is more than the mechanical stability of the aqueous dispersion of the fluorine-containing copolymer found in the prior art. The mechanical stability of the liquid is particularly excellent in terms of the increase rate of the average emulsion particle size.

  In addition, an aqueous dispersion exhibiting excellent mechanical stability can be formed even when the usage ratio is less than half compared with the case of using a conventionally used ammonium perfluorooctanoate emulsifier. The

  Vinylidene fluoride, tetrafluoroethylene and hexafluoroethylene are copolymerized in an aqueous medium in the presence of the surfactant represented by the above general formula. The copolymerization reaction in an aqueous medium is also carried out as a suspension polymerization method, but in order to obtain a desired average emulsion particle size, an emulsion polymerization method is preferred.

The emulsion polymerization reaction is a surface active as an emulsifier generally used at a ratio of about 0.001 to 0.2% by weight with respect to the total weight of the water charged, using a water-soluble inorganic peroxide such as ammonium persulfate or a redox system of it and a reducing agent as a catalyst. In the presence of the agent, the reaction is generally carried out under conditions of a pressure of about 0 to 10 MPa, preferably about 0.5 to 4 MPa, a temperature of about 0 to 100 ° C, preferably about 20 to 80 ° C. At that time, it is preferable to supply the fluorinated olefin mixture to be supplied by the addition method so that the reaction pressure is maintained within a certain range. Further, in order to adjust the pH in the polymerization system, an electrolyte substance having a buffer capacity such as Na ₂ HPO ₄ , NaH ₂ PO ₄ , KH ₂ PO ₄ or sodium hydroxide may be added and used. Furthermore, a chain transfer agent such as ethyl malonate, acetone, isopropanol or the like is appropriately used as necessary.

  The polymerization reaction depends on various polymerization conditions, but generally the reaction is completed in about 1 to 15 hours, which is not much different from the case of using an ammonium perfluorooctanoate emulsifier. After completion of the reaction, the resulting aqueous emulsion is added with a potassium alum aqueous solution, a sodium chloride aqueous solution, a calcium chloride aqueous solution, etc. to coagulate the produced polymer, washed with water, and dried to obtain a fluorinated copolymer. Obtainable.

  When the aqueous dispersion is used for coating materials, the obtained fluorine-containing copolymer is 70 to 96 mol% of vinylidene fluoride and other fluorinated olefins from the viewpoint of coating property and chemical resistance of the coating film. It is preferable to be a copolymer of tetrafluoroethylene and hexafluoropropylene, which are copolymerized so as to have a copolymer composition of 2 to 20 mol% for tetrafluoroethylene and 2 to 10 mol% for hexafluoropropylene. The

  In particular, the average emulsion particle size of aqueous dispersions and the decrease rate of particle size after mechanical treatment, and the decrease of solid content concentration and decrease rate of solid content concentration after mechanical treatment are achieved. For this purpose, it is preferable that vinylidene fluoride is 87 to 89 mol%, tetrafluoroethylene is 5 to 7 mol%, and hexafluoropropylene is 5 to 7 mol%.

  The aqueous dispersion of the fluorinated copolymer having such a copolymer composition has an average emulsion particle size increase rate of 10% or less after passing through a 325 mesh screen 10 times, and is solid. It exhibits excellent mechanical stability with a decrease rate of the partial concentration of 5% or less, and is suitably used for coating material applications in which mechanical processing such as stirring, transfer, metering, pigment mixing, and spraying is performed.

  Next, the present invention will be described with reference to examples.

Example 1
To the pressure reactor made of stainless steel with an internal volume of 10L with a stirrer,
3350g of water
CF ₃ CF ₂ CF ₂ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COONH ₄ 33g
NaOH 1.28g
Ethyl malonate 12.0g
After replacing the interior space with nitrogen gas,
Vinylidene fluoride [VdF] 83.4 mol%
Tetrafluoroethylene [TFE] 5.5 mol%
Hexafluoropropylene [HFP] 11.1 mol%
A mixed gas having the following composition was injected as an initial charge gas until the internal pressure reached about 1.7 MPa · G. After that, when the internal temperature was raised to 80 ° C., the internal pressure became about 2.4 MPa · G.

  Thereafter, an aqueous polymerization initiator solution in which 2.5 g of ammonium persulfate was dissolved in 150 g of water was pressed into the reactor to initiate the polymerization reaction. After the start of the polymerization reaction, a VdF / TFE / HFP (88.1 / 5.8 / 6.1 mol%) mixed gas was further added and maintained in the reactor so that the internal pressure was 2.35 to 2.45 MPa · G. The solid concentration in the reactor was sampled, and when the value reached about 45% by weight (reaction time about 7 hours), the reactor was cooled to complete the reaction. The solid content concentration in the obtained aqueous dispersion was 45.7% by weight.

The obtained fluorinated copolymer in the aqueous dispersion was agglomerated, washed and dried with a 1% by weight aqueous CaCl ₂ solution, and the copolymer composition was measured by ¹⁹ F-NMR. VdF / TFE / HFP = 88.1 / It was 6.0 / 5.9 (mol%). Further, when a 1 wt./vol.% methyl ethyl ketone solution of the fluorinated copolymer was prepared and the solution viscosity ηsp / c at 35 ° C. was measured, the value was 1.2 g / dl.

  Further, when the average emulsion particle size in the aqueous dispersion was measured by a Nikkiso Microtrack Particle Size Analyzer 9340-UPA150 by the laser diffraction / scattering method, the average particle size was 55 nm.

  Also, as the mechanical stability of the aqueous dispersion, the average particle size and solid content concentration of the aqueous dispersion after passing the aqueous dispersion through a 325 mesh metal sieve 10 times were measured, and the solid content concentration was measured. The reduction rate and the increase rate of the average particle diameter were calculated and used as indicators. The solid content concentration after the test was 45.2% by weight, and the average particle size was 59 nm.

Example 2
In Example 1, the amount of the surfactant was changed to 15 g, and a copolymerization reaction was performed.

Example 3
In Example 1, using a mixed gas having a mixed composition of VdF / TFE / HFP = 63/7/30 (mol%) as an initial charge gas, the mixture was injected until the internal pressure became 1.64 MPa · G, and then the internal temperature was 80 When the temperature was raised to ℃, the internal pressure became 2.44 MPa · G, and after the start of polymerization, the VdF / TFE / HFP = (80/10/10 mol%) mixed gas was used so that the internal pressure would be 2.35 to 2.45 MPa · G. Additional addition was carried out, and the reaction was terminated when the solid content concentration reached about 45% by weight (reaction time: about 11.5 hours).

Comparative Example 1
In Example 1, a copolymerization reaction was performed using the same amount (33 g) of ammonium perfluorooctanoate as a surfactant.

Comparative Example 2
In Example 1, after the internal pressure was set to -0.1 MPa · G, a mixed gas having a mixed composition of VdF / TFE / HFP = 49.0 / 35.7 / 15.3 (mol%) was used as the initial charge gas, and the internal pressure was 1.65 MPa · G. When the pressure was increased to G and the internal temperature was raised to 80 ° C., the internal pressure was 2.42 MPa · G, and VdF / TFE / HFP = so that the internal pressure would be 2.35 to 2.45 MPa · G after the start of polymerization. (54.3 / 39.7 / 6.0 mol%) The mixed gas was further added, and the reaction was terminated when the solid concentration reached about 45 wt% (reaction time: about 9 hours).

  For the aqueous dispersions and fluorine-containing copolymers obtained in Examples 2-3 and Comparative Examples 1-2, the copolymer composition of the fluorine-containing copolymer, the solution viscosity, the solid content concentration of the aqueous dispersion, and the average The particle diameter and mechanical stability were measured in the same manner as in Example 1.

The results obtained are shown in the following table together with the results of Example 1.
table
Measurement Item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2
[Fluorine-containing copolymer]
Copolymer composition
VdF (mol%) 88.1 88.0 80.3 88.0 56.0
TFE (mol%) 6.0 6.0 9.9 6.2 40.6
HFP (mol%) 5.9 6.0 9.8 5.8 3.4
Solution viscosity ηsp / c (g / dl) 1.2 1.2 1.2 0.9 1.3
(Aqueous dispersion)
Solid content (wt%) 45.7 44.8 45.3 45.5 45.1
Average particle size (nm) 55 115 62 115 89
Mechanical stability
Solid content (wt%) 45.2 44.2 44.6 42.3 42.6
Decrease rate (%) 1.1 1.3 1.5 7.0 5.5
Average particle size (nm) 59 121 67 132 112
Growth rate (%) 7.3 5.2 8.1 14.8 25.8

From the above results, the following can be said.
(1) Compared with Example 3 which has a copolymer composition that falls within the copolymer composition range of the present invention but does not fall within a particularly preferred range, Examples 1 and 2 have further improved mechanical stability. Yes.
(2) CF ₃ CF ₂ CF ₂ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) When COONH ₄ is used as a surfactant, it is the perfluorocarbon that is the most commonly used surfactant. Compared to the case where ammonium octoate is used, it can be said that a fluorine-containing copolymer aqueous dispersion having more excellent mechanical stability can be obtained even if the amount used is reduced by half (Example 2-Comparison). Example 1).
(3) When it falls within the copolymer composition range described in Patent Document 3 but does not fall within the copolymer composition range of the present invention (Comparative Example 2), a decrease in mechanical stability is inevitable.

Claims (8)

Vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene are represented by the general formula
CF ₃ CF ₂ CF ₂ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COOM
(Wherein M is a hydrogen atom, a lithium atom, a sodium atom, a potassium atom or an ammonium group) 2,3,3,3-tetrafluoro-2- [1,1,2,3,3, 3-hexafluoro-2- (1,1,2,2,3,3,3-heptafluoropropoxy) propoxy] -1-propanoic acid or its salt as a surfactant in a copolymerization reaction in an aqueous medium A process for producing a fluorinated copolymer, characterized in that   A fluorine-containing copolymer produced by the production method according to claim 1.   The fluorine-containing copolymer according to claim 2, having a copolymer composition of 70 to 96 mol% of vinylidene fluoride, 2 to 20 mol% of tetrafluoroethylene and 2 to 10 mol% of hexafluoropropylene.   The fluorine-containing copolymer according to claim 3, which has a copolymer composition of 87 to 89 mol% of vinylidene fluoride, 5 to 7 mol% of tetrafluoroethylene and 5 to 7 mol% of hexafluoropropylene.   A fluorine-containing copolymer aqueous dispersion produced by the production method according to claim 1.   6. The fluorine-containing copolymer aqueous dispersion according to claim 5, wherein the average emulsion particle size in the aqueous dispersion is 30 to 200 nm and the solid content concentration is 40 to 50% by weight.   The fluorine-containing copolymer according to claim 5 or 6, wherein the average emulsion particle size increase rate after passing through a 325 mesh screen 10 times is 10% or less and the solid content concentration decrease rate is 5% or less. Aqueous dispersion.   A coating material comprising the fluorine-containing copolymer aqueous dispersion according to claim 5, 6 or 7.